1. Field of the Invention
This invention relates to the galvanizing of an elongated electrically conductive element by moving it lengthwise through a molten zinc bath. More particularly, the invention relates to a continuous method for galvanizing steel wire or steel strip by drawing it through a zinc bath in an electrically conductive corrodible pan and to the prevention of corrosion of the pan.
2. Brief Description of the Prior Art
It is a usual practice to galvanize a continuous element, such as a steel wire, by drawing the element from a source through a pan containing molten zinc to a take-up reel. A serious practical problem is the short life of the pan which tends to erode and fail, generally at the incoming end in the vicinity of the point of entry of the wire, usually after an average of only 6 to 8 months of use. Sometimes pans fail in only thirty days.
I believe that pan erosion is caused by an electrochemical reaction resulting from a flow of electric current between the element or wire, the zinc and the pan. The current flow is established by thermoelectric potentials developed along the length of the wire as a result of temperature differentials encountered in the galvanizing operation. Briefly, two types of potentials are present: (1) the potential resulting from the absolute temperature of the wire itself (the Thompson effect), and (2) the potential resulting from the temperature difference between the steel wire and the molten material in which it is immersed (the Seeback effect). The potentials due to the latter effect are of greater significance with respect to pan erosion.
In addition to pan erosion, present continuous galvanizing systems suffer other drawbacks which hamper production and decrease production rates. For example, the coating thickness sometimes varies over a wide range, requiring operation at reduced speeds to minimize the coatings below specifications. Variations of more than 75 percent have occurred on samples taken from a single strand of wire. The variations in coatings increase the zinc consumed, raising the zinc cost by several dollars per ton of wire. Also, at times rejects due to low coating are high.